The present invention relates to a method for enhancing the miscibility of halogenated polymers with other immiscible polymers. More particularly, it relates to the use of copolymers of acrylic imides to improve the miscibility of PVC and/or CPVC polymers used in polymer-polymer blends or mixtures.
PVC is a highly versatile material which can be compounded with various types of stabilizers, impact modifiers, lubricants and plasticizers to produce numerous products ranging from rigid opaque containers to flexible transparent films. The ease with which PVC can be molded, extruded, calendered or formed and its low cost has greatly contributed to its commercial success. These copolymers are used extensively in everyday life, especially to produce articles for use in the medical device industry and in the food and drug packaging industries.
Miscibility enhancement of PVC polymers has been a very active field of research in recent years. This interest is due to the fact that it is often desirable to combine or blend PVC based polymers with one or more miscible and/or immiscible polymer based additives to improve some of the properties of the final blend. In addition, when the polymers used in the polymer-polymer blend are miscible, the improved performance characteristics obtained often result in the production of a still wider variety of potentially useful consumer products.
For purposes of this specification, the terms "miscible" or "miscibility" will be used to describe single-phase, polymer blends, or blends which have the physical characteristics of a one-phase blend. Thermodynamically speaking, every polymer has some miscibility in every other polymer, but in some cases the extent of such miscibility is exceedingly low. Therefore, many enhancement techniques have been utilized to improve miscibility. These techniques include the co-polymerization of the desired polymers to each other, either randomly or preferably in the form of A-B blocks acting as miscibility enhancers. In addition, the formation of charge transfer complexes, hydrogen bonding, crosslinking, formation of interpenetrating networks (IPN), ion-ion/ion-dipole interactions, and many other approaches have been used.
Although all of these methods have met with some success in improving the miscibility between various polymer pairs, none is particularly straight forward or consistently reliable. It is therefore highly desirable to provide an improved method for enhancing miscibility which is consistently effective and which does not require the installation of elaborate or expensive equipment for implementation.
Generally, if the resulting blend exhibits a single glass transition temperature, it is considered to be miscible. However, if the glass transition temperatures of the individual polymers comprising the blend are initially in close proximity, a single glass transition temperature may be obtained with an immiscible system. When this is the case, the fact that two polymers are immiscible may be shown by testing the properties of the final blend such as mechanical, morphology, etc.
In most cases, an immiscible polymer blend will exhibit opacity, delamination, double glass transition, or a combination of these properties. However, if the refractive indices are the same for the two polymers, even the immiscible blend will appear transparent.
These and other objects are attained by the present invention wherein at least 5 weight percent of a known acrylic imide copolymer is added to a mixture of a PVC based polymer and one or more essentially immiscible polymers to produce a final resin composition or blend possessing properties analogous to those expected for a single-phase material.